1. Field of the Invention
The present invention relates to an image forming apparatus of electrophotographic type such as a copying machine, a laser beam printer and the like.
2. Related Background Art
Image forming apparatuses wherein, after a toner image formed on a moving image bearing member is transferred to a transfer material, then residual toner not transferred to the transfer material and remaining on the image bearing member is cleaned and such cleaning operation is repeated, are well known. In such an image forming apparatus, in order to remove the residual toner, a cleaning blade made of elastic material such as urethane rubber has been widely used as a cleaning means for removing the residual toner, since it is compact and is simple in construction, which leads to make the apparatus inexpensive.
An example of one of such conventional cleaning devices is shown in FIG. 6.
A cleaning device 8 extending in a direction perpendicular to the plane of FIG. 6 is arranged in parallel with and in the proximity of an image bearing member 2 rotated in a direction shown by the arrow. The cleaning device 8 includes a cleaning blade 13 a free end of which is urged against a surface of the image bearing member to scrape and remove the residual toner generated at a transfer station and reached to a cleaning station. The removed toner is guided by a dip sheet 10 to reach a toner reservoir portion of the cleaning device and then is discharged from the reservoir portion by a convey screw 14. Incidentally, it should be noted that elements for forming an image such as a primary charger, an image signal applying means, a developing device, a transfer means and the like are arranged around the image bearing member 2.
However, since the residual toner remaining on the image bearing member has a charge, the toner is adhered to the surface of the image bearing member by a strong electrostatic absorption force. Thus, since the cleaning blade must remove the toner particles from the surface of the image bearing member while overcoming the electrostatic absorption force of the toner particles to the image bearing member, the cleaning blade must be urged against the surface of the image bearing member with a strong force. In addition, in many cases, the cleaning blade is urged against the surface of the moving image bearing member with the free end (edge) thereof directed toward a direction resisting the movement of the image bearing member, with the result that the great friction force is generated between the blade edge and the image bearing member. The toner scraped from the image bearing member by the blade acts as the lubricant between the image bearing member and the blade edge, thereby reducing the friction force. In fact, however, the blade and/or the image bearing member were worn, or sometimes, the edge of the blade was turned up in the rotational direction of the image bearing member.
To eliminate such inconvenience, various techniques in which coating material having a coefficient of friction small than that of the cleaning blade is coated on the surface of the cleaning blade have been proposed (for example, refer to U.S. Ser. Nos. 710,772 and 059,852).
As methods for applying the liquid coating material on the surface of the blade, there are a method for spraying the coating material on the blade surface, a method for dipping the blade into the coating material contained in a bath and the like. Although such methods have advantages and disadvantages, the cleaning blade manufactured by the dipping method has been widely used, because it is important to maintain the flatness of the coated surface of the cleaning blade and such flatness can relatively be easily obtained by the dipping method.
In the cleaning blade manufacturing method using the dipping coating technique, for example, after a cleaning blade made of urethane rubber is dipped into the solution including nylon resin and alcohol, the blade is dried to evaporate the alcohol, thereby forming the nylon coating layer on the surface of the blade. When the cleaning blade having the surface coating layer is manufactured in this way, as shown in FIG. 5, a bead a of the coating material is formed on the edge portion of the blade. To eliminate such coating material bead a, as shown in FIG. 5, the edge portion of the blade is cut off. In this way, the accuracy of the edge of the blade is obtained.
However, the inventors found that, as shown in FIG. 5, a bead of the coating material was also formed slightly in a position b on the blade surface out of the blade edge. Although the size of such bead b differs depending upon the dipping condition, in the actual measurement, it was found that such bead had a height of about several microns and a width of 600 microns at the maximum. If such bead b is abutted against the surface of the image bearing member, since flatness of the blade cannot be maintained, the cleaning ability will be worsened.